In a healthy person, blood oxygen is automatically regulated through his or her respiration rate. As a person's activity level increases they breath faster and more deeply so that their respiratory system is able to deliver a greater amount of oxygen to their body. Diminished oxygen uptake into the body generally results from a partial disability of the pulmonary system, i.e., the lungs, caused by a variety of physiological ailments. Persons with pulmonary disabilities very often require enrichment of atmospherically available oxygen by artificial supplementation from a source of oxygen gas. The need for oxygen supplementation is particularly acute for persons suffering from Chronic Obstructive Pulmonary Disease (COPD) such as, emphysema.
In advanced COPD patients, the respiratory system is simply unable to supply the necessary oxygen levels required during increased activity. As a result, an acceptable level of oxygen must be maintained by enriching the oxygen level in the air being delivered to the lungs. This is often accomplished by placing a supply of oxygen at a central location and attaching one end of a long hose to the supply and the other to the patient. A common delivery system for supplemental oxygen is a tank reservoir containing pressurized medical quality oxygen. This type of tank is normally outfitted with a flow regulator comprising a flow control valve which governs the rate of oxygen flow, i.e., volume, from the tank to a nasal cannula, breathing mask, or transtracheal oxygen delivery system. With this type of conventional connection, the flow of gas is normally constant during both inhalation and exhalation.
The positioning of the control valve for the supply of oxygen at a distance from the patient has created problems in the art. Just as a healthy person's oxygen demand varies with the level of activity being undertaken, so does the demand for oxygen vary for COPD patients. The only way to deliver more oxygen to COPD patients, when such is required during periods of increased activity, i.e., walking to the bathroom, up steps, etc., has been to adjust the oxygen flow at the source prior to undertaking the activity. This has been accomplished either by the patient having to add the additional steps of walking to the oxygen source first, to adjust the flow and then carry on the activity, or to call to a family member or other person to assist them by increasing the flow. This causes logistical problems for the patient. Often, COPD patients merely maintain the flow rate of the oxygen at a higher level than necessary, i.e., during increased activity and at rest, which creates a dependency upon the higher oxygen levels that is similar in effect to the use of a habit forming drug.
In view of the large number of persons in society who require such oxygen supplementation, much effort has been dedicated to the development of devices which insure delivery of adequate supplemental oxygen. Exemplary prior art devices for detecting a patient's oxygen demand and providing for an increase in flow are disclosed in U.S. Pat. Nos: 4,567,888, issued to Robert, et al.; 4,744,356, issued to Greenwood; 5,024,219, issued to Dietz; 5,137,017, issued to Salter; 5,271,389, issued to Isaza, et al.; 5,315,990, issued to Mondry; 5,323,772, issued to Linden, et al.; 5,365,922, issued to Raemer; and 5,390,666, issued to Kimm, et al. Many of these devices rely upon sensors placed under the person's nose or otherwise on a person's face for detecting the flow of oxygen. Such sensors may prove irritating to the patient.
Some prior art systems employ a sensor connected to a controller which, in turn, is connected to a solenoid valve on an oxygen tank. Upon sensing inhalation, by pressure changes, etc., the sensor signals the controller to energize the solenoid, thus opening the valve and inducing oxygen flow. This arrangement may not provide oxygen to the user where there is a system failure or allow for a "ramp-down" period of gradual reduction in oxygen flow during a recovery period after increased activity. Also, these systems are used for the purpose of conserving oxygen rather than supporting the patient's need for varying levels of oxygen supply.
Other prior art oxygen delivery devices rely upon an oximeter to measure blood oxygen saturation. These devices adjust valves to deliver increased flow after oxygen saturation begins to decrease. Unfortunately, devices which rely upon a direct measure of blood oxygen levels are often found to be inadequate since the delivery of oxygen often falls behind the demand by the time required for the person's blood to circulate through the body. Also, these systems often rely upon the use of a finger sensor that is uncomfortable for the patient.
There is a need for an oxygen flow control device and method which provide increased oxygen flow rates to a patient, as needed, during increased activity, and which provides for "ramp-down" and "fail-safe" operation.